1. Field of the Invention
The present invention relates to a transmission rate control method for controlling a transmission rate of uplink user data to be transmitted by a mobile station via a logical channel, and a mobile station.
2. Description of the Related Art
In a conventional mobile communication system, in an uplink from a mobile station UE to a radio base station Node B, a radio network controller RNC is configured to determine a transmission rate of a dedicated channel, in consideration of radio resources of the radio base station Node B, an interference volume in an uplink, transmission power of the mobile station UE, transmission processing performance of the mobile station UE, a transmission rate required for an upper application, and the like, and to notify the determined transmission rate of the dedicated channel by a message of a layer-3 (Radio Resource Control Layer) to both of the mobile station UE and the radio base station Node B.
Here, the radio network controller RNC is provided at an upper level of the radio base station Node B, and is an apparatus configured to control the radio base station Node B and the mobile station UE.
In general, data communications often cause burst traffic compared with voice communications or TV communications. Therefore, it is preferable that a transmission rate of a channel used for the data communications is changed high-speed.
However, as shown in FIG. 1, the radio network controller RNC integrally controls a plurality of radio base stations Node B in general. Therefore, in the conventional mobile communication system, there has been a problem that it is difficult to perform high-speed control for changing of the transmission rate of channel (for example, per approximately 1 through 100 ms), due to processing load, processing delay, or the like.
In addition, in the conventional mobile communication system, there has been also a problem that costs for implementing an apparatus and for operating a network are substantially increased even if the high-speed control for changing of the transmission rate of the channel can be performed.
Therefore, in the conventional mobile communication system, control for changing of the transmission rate of the channel is generally performed on the order from a few hundred ms to a few seconds.
Accordingly, in the conventional mobile communication system, when burst data transmission is performed as shown in FIG. 2(a), the data are transmitted by accepting low-speed, high-delay, and low-transmission efficiency as shown in FIG. 2(b), or, as shown in FIG. 2(c), by reserving radio resources for high-speed communications to accept that radio bandwidth resources in an unoccupied state and hardware resources in the radio base station Node B are wasted.
It should be noted that both of the above-described radio bandwidth resources and hardware resources are applied to the vertical radio resources in FIGS. 2(b) and 2(c).
Therefore, the 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2), which are international standardization organizations of the third generation mobile communication system, have discussed a method for controlling radio resources at high speed in a layer-1 and a media access control (MAC) sub-layer (a layer-2) between the radio base station Node B and the mobile station UE, so as to utilize the radio resources effectively. Such discussions or discussed functions will be hereinafter referred to as “Enhanced Uplink (EUL)”.
Radio resource control methods that have been discussed in the “Enhanced Uplink” can be broadly categorized into three as follows. The radio resource control methods will be briefly described below.
First, a radio resource control method that is referred to as “Time & Rate Control” has been discussed.
In such a radio resource control method, a radio base station Node B determines a mobile station UE which can transmit user data and a transmission rate of user data of the mobile station UE per a predetermined timing, so as to signal information relating to a mobile station ID as well as the transmission rate of user data (or a maximum allowable transmission rate of user data).
The mobile station UE that is designated by the radio base station Node B transmits user data at the designated timing and the transmission rate (or within a range of the maximum allowable transmission rate).
Second, a radio resource control method that is referred to as “Rate Control per UE” has been discussed.
In such a radio resource control method, if there is user data that should be transmitted to the radio base station Node B, each mobile station UE can transmit the user data.
However, the maximum allowable transmission rate of the user data, which is determined by the radio base station Node B and signaled to each mobile station UE for each transmission frame or each of a plurality of transmission frames, is used.
Here, when the maximum allowable transmission rate is signaled, the radio base station Node B signals the maximum allowable transmission rate itself, or a relative value thereof (for example, three values of “Up command”, “Down command”, and “Hold command”), at this timing.
Third, a radio resource control method that is referred to as “Rate Control per Cell” has been discussed.
In such a radio resource control method, a radio base station Node B signals a transmission rate of user data, which is common among mobile stations UE in communication, or information needed to calculate the transmission rate, and each mobile station UE determines a transmission rate of user data based on the received information.
Although a downlink control signal load and a transmission rate control load in the radio base station Node B or the like exist, as proposed in “Time & Rate Control” and “Rate Control per UE”, to control the transmission rate of the each mobile station UE, respectively, can be a good control methods for improving radio capacity in an uplink.
As shown in FIG. 3, “Rate Control per UE” is configured to control the transmission rate of user data using an “Absolute rate Grant Channel (AGCH)” and a “Relative rate Grant Channel (RGCH)”.
By using the RGCH frequently, it is possible to simplify the control signals transmitted from the radio base station Node B for controlling the transmission rate of user data, and to reduce effects in a downlink, which is caused by the control signals.
The detailed performance of the transmission rate control using the RGCH, which includes three values of an “Up command”, a “Down Command” and a “Hold Command”, is described in Non-Patent literature 1 (3GPP TSG RAN R2-050229).
As described in the Non-Patent literature 1, the method that instructs to increase, decrease or hold the last transmission rate of HARQ is common.
Further, in each cell, the interference volume of a mobile station UE designating another cell as a serving cell (a non-serving mobile station) have to be considered.
When the interference volume from non-serving mobile station UE is increased, in each cell, the RGCH including the “Down Commend” for decreasing the transmission rate of user data transmitted from the non-serving mobile station UE is transmitted.
Here, the RGCH for non-serving mobile station UE includes binary of a “Down Command” and a “Do Not Care Command”, and is different from the RGCH transmitted from a serving cell set.
Furthermore, as described in Non-Patent literature 2 (3GPP TSG RAN TS25.309 V.6.1.0), if at least one “Down Command” is received during a communication with the serving cell and more than one non-serving cells, the mobile station UE is configured to prioritize the received “Down Command”, so as to control the transmission rate of user data.
Accordingly, as described above, in the EUL, it is possible to change a transmission rate of uplink user data in each mobile station UE at high-speed, and dynamically, using an interference level in a radio link and processing resources of the radio base station Node B and the like.
However, in each logical channel, Quality of Service (QoS) has been set.
For Example, a logical channel used for a voice communication can be low-speed of a few kbps to few dozen of kbps. However, the voice communication needs to be received by a receiver without a delay.
In addition, a logical channel used for an image communication and the like needs a transmission rate having predetermined level. Here, the transmission rate having predetermined level can be expressed as a “Guaranteed Bit Rate (GBR)”.
However, there has been a problem that a transmission rate of user data may be below the GBR of a logical channel, when a mobile station UE, which transmits user data via the logical channel having the GBR, controls the transmission rate of user data by following a received “Down Command”.